The specific aims of our current research reflect both our continued interest in dissecting the functioning of the Drosophila sex determination hierarchy and our interest in understanding how information from the sex determination hierarchy is integrated with information from developmental hierarchies specifying other aspects of development (e.g. segment identity, tissue and cell type, etc.) to insure the proper temporal, spatial, and sexual expression patterns of downstream genes. We are addressing the following topics: I. How do the TRA and TRA-2 proteins function together with the housekeeping splicing machinery to regulate doublesex pre-mRNA splicing? II. The intersex (ix) gene functions in females where it acts together with dsx at the bottom of the sex determination hierarchy. We are molecular characterizing the ix gene with the aims of determining (1) the molecular function of the IX protein and (2) the basis of ix's female- specificity. III. How do the products of the intersex, doublesex and hermaphrodite genes work together to specify appropriate expression of specific terminal differentiation genes? IV. How is genital imaginal disc development controlled? Specific topics include: A. How are the progenitor cells of the male genital, female genital and anal primordia, which comprise the genital disc, established during embryogenesis? We are characterizing both known embryonic patterning genes, and new genes identified in an enhancer trap screen, to elucidate the regulatory hierarchies that govern the establishment and specification of the precursors of the three genital disc primordia. B. How is patterning of the mature third instar genital disc achieved? Our current efforts focus on the potential roles of the decapentaplegic, wingless, and fringe genes in P/D and D/V patterning. D. Every embryo has both female and male genital primordia, only one of which proliferates. We are addressing how the repression of the inappropriate genital primordia is achieved. D. To better understand the role of the sex determination hierarchy in the genital disc, genes expressed sex-specifically in this disc are being characterized. V. How has the process of sex determination evolved?